New universal serial bus (USB) power-delivery (PD) and Type-C specifications have been released that enable delivery of higher electrical power over new USB cables and connectors. The intent for this technology is to create a universal power plug for laptops, tablets and other devices that may require more than a 5V power supply.
The USB-PD specification defines a communication link between ports connected via a USB-PD cable and connectors. The communication is designed to be half-duplex and packet-based. The packets contain various information that enables the source port and sink ports to communicate and negotiate the voltage and current the source port will provide to the sink port. The ports can negotiate to switch roles (i.e., the source port to become the sink port and vice versa).
The underlying communication in the USB PD specification is Biphase Mark Coding (BMC). The USB-PD communication goes over a different wire (e.g., the secondary Cable Connection (CC2) wire) rather than the USB data wires. For USB Type-C cables up to 15 W of power can be delivered even without USB PD messaging by controlling the DC voltage on the CC pin.
FIG. 1 shows a block diagram of a known USB PD system 100 after downstream facing port/source (DFP) 110 to upstream facing port/sink (UFP) 120 attachment via a cable 105 that utilizes BMC signaling for PD. The DFP 110 is shown implemented with a resistive pull-up (shown as Rp) to its CC pin, which can also be a current source. A power supply 125 supplies power to the Vbus line that is received across the load (or power sink) 130 via the cable 105. A DC voltage on the CC line is established by the Rp on one end of the cable 105 and a resistive pull-down shown as Rd between the CC pin and ground on the other end of the cable. The power supply is shown as a 3.3V DC supply coupling through RP and Rd. There are other lines that may be present in the cables shown as data lines that are not relevant to this Disclosure.
Some battery-operated mobile devices utilize more than one USB Type-C receptacle and the USB PD protocol. Some systems also implement the Type-C and PD capabilities using an analog frontend or port controller coupled to a microcontroller (or other processor) that acts as a master in the PD system. In typical scenarios the port controller is a slave to the microcontroller, where the microcontroller tells the port controller when to turn on or off any power-path switch or input/output pin typically referred to as a general-purpose input/output (GPIO) pin. The microcontroller may use the same Inter Integrated Circuit Communications (I2C) bus to control multiple (e.g., 2) port controllers.
There are cases where such a load's 130 battery is removed or drained of any charge. This is referred to herein as the dead-battery scenario. In the dead-battery scenario, the PD system 100 needs a way to receive power from the VBUS pin of one (and only one) of its Type-C receptacles (or connectors). The port controller connects the VBUS pin of the Type-C receptacle into the power system of the device so that it can begin functioning properly. This means that the port controller needs to take some autonomous action in the dead-battery scenario. The port controller detects this dead-battery scenario by the presence or absence of VDD at its VDD supply pin. If no voltage is applied to the VDD supply pin which is typically directly connected to a positive DC power supply (e.g., 3.3 V), but power is applied to the VPWR pin of the port controller, then the port controller operates as if it is in a system with a dead-battery.
In some system architectures there are first and second port controllers in a system architecture where both port controllers are driving a power-path switch for the same power-path. The power-path is designed so that only one port's power-path switch may be closed, where the design intends for “collisions” to be avoided. Collisions may be avoided by coupling the respective port controllers so that they recognize each other and the first port controller that can provide power to the power system sink takes control of supplying power. Known system architectures having first and second port controllers and at least one power-path switch coupling to a power path sink (load device) typically use current sources and voltage detectors to measure the voltage level to avoid collisions.